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Inside the Atom Chapter 1 Models of the Atom • What is a scientific model? ▫ ▫ ▫ ▫ a representation of an object or system can be used to make a prediction can be tested must be able to explain as many characteristics of the observations as possible ▫ must be as simple as possible ▫ all models have limitations Models of the Atom A. Greek philosophers devised a theory of atoms, or tiny particles. B. John Dalton combined the idea of elements with the Greek theory of the atom. 1. 2. 3. 4. 5. Matter is made up of atoms. Atoms cannot be divided into smaller pieces All atoms of an element are exactly alike. Different elements are made of different atoms. Dalton’s theory was tested by William Crookes and his cathode-ray tube experiment. • The negatively charged electrons are attracted to the positive plate and repelled by the negative plate C. J.J. Thompson discovered negatively charged particles, electrons, which are a part of every atom. 1. Thompson revised Dalton’s model to include a sphere with positive charge and negatively charged electrons spread evenly within the positive charge. 2. The negatively charged electrons and the positive charge in the sphere neutralize each other. D. Earnest Rutherford tested Thompson’s model, which was found to be an inaccurate model of the atom. Golf foil experiment Only a large positive charge would cause the particles to bounce back! D. An atomic model with a nucleus was developed. 1. The positively charged proton is located in a very small space at the center of an atom 2. Most of an atom is empty space occupied by nearly massless electrons. 3. Electrically neutral particles, neutrons, are also located in the nucleus. 4. The number of electrons equals the number of protons in an atom. E. The electron cloud model explains the unpredictable wave behavior of electrons, which could be anywhere in the area surrounding the nucleus. • We are going to model our own atom according to the electron cloud model. • Half will be protons and half will be electrons. • The entire room is our atom. The Simplest Matter A. Elements – matter made up of one kind of atom. 1. There are 112 known elements 2. 90 naturally occurring elements, 25 synthetic elements – made by scientists B. Periodic Table – Chart that organizes and displays information about the elements. 1. Atomic number – the top number in the element’s periodic table block a. Tells the number of protons in the nucleus of each atom of that element b. The number of protons remains constant in every atom of an element. 2. Isotopes – atoms of the same element that have different numbers of neutrons 3. Mass number – number of protons plus number of neutrons 4. Atomic mass – the number found below the element symbol a. The average mass of an atom of an element b. The unit used for atomic mass is the atomic mass unit, which is given the symbol u. C. Elements fall into three general groups characterized by similar properties. 1. Metals – most of the elements a. b. c. d. e. Shiny luster Good conductors of heat and electricity Most are solids at room temperature Malleable , or can be shaped Ductile, or can be drawn into wires without breaking 2. Nonmetals – found on the right side of the periodic table a. b. c. d. e. Dull in appearance Poor conductors of heat and electricity Many are gases at room temperature Brittle, cannot change shape without breaking 96 percent of the human body is made up of nonmetals. 3. Metalloids – found between the metals and nonmetals on the periodic table a. Have characteristics of both metals and nonmetals b. Do not conduct heat and electricity as well as metals c. All are solids at room temperature Compounds and Mixtures A. Substance – matter that has the same composition and properties throughout B. Compound – substance whose smallest unit is made up of atoms of more than one element 1. Formula – tells which elements make up a compound as well as how many atoms of each element are present a. b. The subscript number tells how many atoms of the preceding element are in the compound No subscript is used when only one atom of the element is present 2. A given compound is always made of the same elements in the same proportion. Questions: • H2O – How many elements are there? • C6H12O6 – How many oxygen atoms are there? • KOH – How many atoms are there? • C2Cl3F3 – How many elements are there? – How many Carbon atoms are there? • NaCl – How many elements are there? Bonus question: • C10H7N3S – How many atoms are there? • Mixture – two or more substances mixed together which don’t make a new substance ▫ Unlike compounds, the proportions of the substances can be changed without changing the identity of the mixture ▫ Examples: air, blood… ▫ Can separate mixtures easily ▫ Homogeneous mixtures – the same throughout ▫ Heterogeneous mixtures – you can see the different parts